Zhang Sanfeng created the Heaven Sword Dragon Sabre poem art in one night...and from the looks of how Zhang Cuisan used it, it was actually powerful and at least comparable to all the other arts he has learned. This suggests that he either learned inferior arts in the past (which is a bit unlikely), or that Zhang created a very powerful art in the span of a few hours.
Has any other character done that ? Hong Qi Gong and Ouyang Feng created stances to counter each other, but that's a bit different than creating a whole martial art with hundreds of variations.
The scene where Zhang invents it is kind of silly, where Zhang Cuisan memorizes his every movement, even though a move could easily just be a test move from Zhang Sanfeng to see how it works and completely useless in real life. There also wasn't any formula or specific inner workings to it since Cuisan just watched and learned it without need for explanation.
And on a last note, it's ironic that when Zhang Sanfeng creates this art it's a glorious moment since he is juxtaposing martial arts and writing, but hundreds of years later Ren Woxing mocks the 2nd Master of Plum Manor for restricting his martial arts with words/writing styles when an art would obviously be more powerful if it had no limitations in needing to follow the character strokes.